Conventionally, it has been possible to simulate an image of a knitting fabric or a weaving fabric by assuming a yarn that is to be used without actually manufacturing the fabric (see Japanese Unexamined Patent Publication JP-A 07-70890 and WO98/16823, for example). Also, the applicant has filed Japanese Patent Application No. 2001-310559 that relates to a method and an apparatus in which image data of a knitting yarn is input to simulate an image of a knitting fabric knitted by using the knitting yarn. The technique of this application makes it possible to easily simulate an image of a knitting fabric knitted by using a fuzzy knitting yarn of an irregular shape called “fancy yarn”.
Compared with a weaving fabric, a knitting fabric generally uses a thicker yarn and has coarser knitting stitches. For this reason, the use of a fancy yarn as a knitting yarn can realize, for example, a peculiar design effect or feeling. For a fancy yarn, a twisted yarn is sometimes used that is produced by twisting a plurality of yarns. A product also has been introduced that can display an image of a fancy yarn weaving fabric or knitting fabric using a fancy yarn or a yarn obtained by further twisting fancy yarns (see Chrittiane Szezesny and other two authors, “Simulation of Fancy Yarns on the Screen”, in Fabric Forming, ITB, March 1991, pp. 73-74, for example). With the use of an image of a twisted yarn in the technique proposed in Japanese Patent Application No. 2001-310559, it is possible to simulate an image of a knitting fabric using the twisted yarn. Also, it has been reported that when yarns are twisted, the cross-section shapes of the yarns are compressed (see A. Grishanov and other four authors, “The Simulation of the Geometry of Two-component Yarns Part I: The Mechanics of Strand Compression: Simulating Yarn Cross-section Shape”, in J. Text. Inst., Textile Institute, 88 Part 1 No. 2, 1997, pp. 118-131, for example).
FIGS. 1 to 5 of the article (Chrittiane Szezesny and other two authors, “Simulation of Fancy Yarns on the Screen”, in Fabric Forming, ITB, March 1991, pp. 73-74) show images of (1) a single fancy yarn, (2) a fancy yarn obtained by twisting a plurality of such fancy yarns, and (3) a fabric using such fancy yarns. Some figures do not include (2) a fancy yarn obtained by twisting. Although it is not clarified how these images are simulated, one of the authors of the article (Chrittiane Szezesny and other two authors, “Simulation of Fancy Yarns on the Screen”, in Fabric Forming, ITB, March 1991, pp. 73-74) is listed as an inventor of WO98/16823, and thus it is presumed that the simulation is performed by using the technique disclosed in WO98/16823.
In the technique disclosed in WO98/16823, a three-dimensional model of a three-dimensionally scanned yarn is formed by combining the position coordinates of a plurality of points set on the surface and the orientation of the surface region including the points. A numerical model is processed to calculate three-dimensional spatial coordinates through which the central line of the yarn passes in a weaving fabric or a knitting fabric, and the central line of the three-dimensional model of the yarn is deformed in accordance with the central line of the numerical model. At that time, the points set on the surface of the three-dimensional model of the yarn are also displaced in accordance with the central line, so that an image of the yarn is displayed as a collection of such points, and the simulation is thus performed.
When the three-dimensional model of the yarn is created, it is expected that an image of the actual yarn is faithfully reflected by narrowing a gap between the points on the surface to make the density therein high. However, when the number of points becomes large, a time necessary for processing an image becomes long. Furthermore, since a fancy yarn is characterized by comprising, for example, fine fuzz that exists in an irregular manner and the fuzz sticks outward on the surface, the fancy yarn is difficult to reflect on a three-dimensional model by a method such as described above.